Late reproduction behaviour in Sardinia: spatial analysis suggests local aptitude towards reproductive longevity

Evolution in human life-history traits is influenced by environmental factors and, when genetic components underlie the relations, by micro-evolutionary forces. Age at reproduction is largely influenced by the familial cultural context and socio-economic level, besides the maternal well-being and genetic background. Sardinian population is characterized by historico-geographical isolation, and differentiates from Italian mainland and other European populations in bio-demographic and cultural characteristics, among which the tendency to delay maternity persisting through generations. In our study we investigated whether, in Sardinia, areas of “reproductive longevity” exist, where a higher-than-average incidence of late maternities combines with a lower-than-average cost in terms of perinatal death. Data from the Italian Central Institute of Statistics regard all 1980-96 Sardinian births. Using spatial analysis of late maternity (proportion of babies born to ³35year-old mothers) and associated perinatal mortality (proportion of babies stillborn and dead within 0-6 days in ³35year-old mothers) we aimed at singling out areas where the indicators run high and low, respectively. The perinatal mortality cost associated with the advanced maternal age (OddsRatios [95%CI]) was evaluated through multiple logistic regression models. We identified central inland excess areas qualified by higher incidence of late maternities (27% vs 22% in non-excess area), and lower cost in perinatal mortality (OR=1.38[1.04-1.84] vs OR=1.74[1.55-1.96] in non-excess area). In these “reproductive longevity” areas the inbreeding coefficient was 3.7 fold higher than in the non-excess areas, suggesting possible population homozygosity in genetic factors affecting the trait. Further and deeper investigations on biological and environmental determinants could focus on these target areas.